Telephone system



Oct'. 18, 1932. BQWNE 1,882,753

TELEPHONE SYSTEM Filed May 29, 1931 5 Sheets-Sheet J O 9 Q5 N l2INVENTOR L.J. BOWNE 8) W7 Oet. 18, 1932. J, BQWNE 1,882,753

TELEPHONE SYSTEM Filed May 29. 1931 5 Sheets-Sheet 3 'g-"IIIHI INVENTORL J. BOWNE Y A Tm/PNEY Patented Oct. 18, 1932 U ITED stares PATENTOFFICE LANeEoR-n J. BOWNE, OE HOWARD BEACH, EW YORK; 'AssIGNoR'To BELLTELEPHONE LABORATORIES, INCORPORATED, OE NEW YORK, N. Y; A CORPORATIO OENEW YORK TELEPHONE SYSTEM Application filed May 29, 1931. Serial NO.540,839.

nections established by means of a local op-I erators cordbetween alocal subscribers line and a line to a distant exchange, when the localsubscriber hangs up his receiver on.

the switchhook to disconnect, the connection through the cord is split.Thisis for the purpose of preventing the subscribers station from beingsignaled in case a call is incoming over the line used in thisconnection before the operator has removed the cordfrom the localsubscribers line. Heretofore', this;

splitting has been done by the Operation of a slow-to-operate relaywhich operated when the subscriber replaced his receiver on the,switchhook. The operation of this relay was.

made slow in order to prevent it from operating during momentaryopenings Ofthe connection such as occur when the switchhook is flashedbythe local subscriber or when supervision occurs from the distantofiice. In modern telephone practice the talking current has beenincreased in circuits of this ,lrind which made it'more difiicult forthis slow-to-operate relay to function with a desired uniformity underall conditions of volt- I variations which may occur due to thedifferent transmission characteristics of the connected lines.

It is a feature of this invention to overcome such variations in theperiods of delay of the splitting of the cord by providing a circuitarrangement whereby a slowtorelease relay is maintained operated whilethe connection is established 'and permitted to release when thesubscriber replaces his receiver on the switchhook for the release ofthe connection. The circuit for this slow-to-release relay is controlledby the usual supervisory relay included in the line connection. By thismeans the periods of delay in splitting of the distant exchange.

cord are made uniform as they are controlled by the slow'-to-releasecharacteristic of this relay independently of the voltage variations onthe line.

i In establishing a connection to a distant exchange over a line thecircuit for the above mentioned splittingrelay must be put under controlof the supervisory relay when the through connection is finallycompleted and the call is answered by the operator .at the Thissupervisory relay, however, operates as soonas the local operatoranswers the call from the local subscriber for supervisory purposes, itis then momentarily released, and finally transferred under control ofthe battery and ground connection established over the tip and ringconductor when the operator at the distant exchange answers the call. Itis, therefore, a further feature of this invention in order to preventthe false release of the splitting relay during the transfer period toestablish circuit conditions whereby the splitting relay 'is operatedand held by a local battery and ground connecton in the cord as soon asthe connection to the distant exchange line, is established and thentransferred to the control by the supervisory relay when this latterrelay is finally operated.

When the local subscriber hangs up his so receiver on the switchhook tocause the connection to the distant exchange to, be split, a battery andground connection is established from the cord to the subscribers linefor the purpose of permitting the subscriber. 5 r to make a recall onthe connection. Under these circumstances, a surge of current may occurin the circuitdue to the battery and ground connection chargingthecondenserin the subscribers telephone set. It is a go feature of thisinvention to prevent this surge from'disturbing the established circuitconditions in the cord, such as for example, to falsely establish abridge across the connection to cause a false signal at the centralvoffice. To prevent such disturbances acirouit arrangement has beenprovided forshort-circuiting one winding of the battery feed relay thatwould initiate such false signaling by its operation, due to its beinginconnection, the-connection through the cord is reestablished :by thesplitting relay-independently of the supervisory relay in the cord andthe splitting relay is not placed under control of the supervisory relayuntil the supervisory relay isoperatedii'n response to current receivedoverthe established connection from the distant exchanges. Hence in caseof along line connection :where the transmission characteristics maycause the operation of the supervisory ,rel-ay tobede- "layed thisdelay;will notfinterfere with the proper function of the splitting relay inestablishing a through connection. This is accomplished by'having thespecial battery feed relay operate when the subscriber lifts his'receiver'fromthe switchhook and having this relay shunt thesupervisoryrelayto per- ".mit the operation of the splitting relay.

WVh'en'the currentis received from the dis- "'tant exchangethesupervisory relay operates and causes'the control over the splittingre- Llay .to 'be transferred to the supervisory relay.

Another :feature of this invention is an arrangement whereby, when aconnection is established to a-centra'l otlice,the subscribers telephoneis shunted while the battery and ground connection for the tip andringconductors is;shift.ed from a supply in the cord to a'supplyatthecentral office. This is to jprevent clicks in the subscribers receiverduring this transfer. The arrangement is such that when the cord isextended'to the central ofiice trunk a short circuit is placed throughthe cord circuit. Then when the connect1on is extended in the centraloflice to the across'the subscribers 'line, the current sup- "ply atthecord is then removed and a bridge is placed-across the tlp and ringconductors,

whereupon-the short circuit is removedand the tip, and'ring conductorsare connected current supply-thereat thebridge is removed. It is anotherfeature of-this'lnvention to short-circuit the operators receiver for ashort interval while the operator answers a callmcoming over'a trunk inresponse to the operation of'tlietalking keyin the cord and"itheinsertion of the answering plug ofthis 7 cord intothe trunk jack.

It'isanother featureof this invention to short-circuit the operatorsreceiver for a short {interval while she answers a call in comingoverthe trunk to which a cord is 'already connected. "This short circuit istestab'lished'bythe same means, namely, the

operation of the talking key and the condi- 1neans employed forshort-circuiting the receiver'is also used asa means for tripping theringing at'th'e central ofiice when the operator answers the call on atrunk, regardless of whether the call-is answered over a trunk to :whichthe cord employed'is connected or not, at the time of the call. This isaccomplishedtby the establishing of abridge across the tip and ringconductors of the trunk for a short interval.

It is another feature of this invention to provide an arrangementwhereby the same means that is used for 'short-circuiting the receiverwhile answering acall or for tripping the ringing is employed forshort-circuiting the receiver during dialing over a central officeconnection and for maintaining the receiver short-circuited ashortinterval after dialingto prevent disturbances or clicks in the-receiverdue'to operations atthe central offfice effected by'the dialing.

Another feature o'f'this invention is an arrangement in tie linesemployed in systems of this kind for automatically removing therepeating coil from across tie'lineconductors when ringing isappliedtothe line on outgoing calls and thereby remove'the drain on the ringingcurrent. This is accomplished by means of an alternating currentresponsive relay actuated by the ringingcurrent which relay in turncauses another relay to release and open a connection for the repeatingcoil and establish through connections for the line conductor to permitthe ringing current to pass out on the line.

Another-feature of this invention is an arrangement in tie lines used insystems of this kind that have a separate jack for dialing a distantstation, for preventing false impulses or interruptions of theconnection through the .tie line to the distant station from occurringwhen the connection is switched from the .talking jack to the dialingjack. This is accomplished by means whereby the tip and Iring terminalsof the dialing jack and the tip and ring conductors of the tie line areshort-circuited when a cord circuit is connected to the dialing jack andmeans whereby Whenthe cord has-been prepared for dialing the followingfunctions are caused to take place in the order named: To disconnect thetie line fromthetalking jack, to remove-the short circuit from thedialing jack terminals, to establish a through connection for the tipconductor, to establisha through connection for the ring conductor andto remove the short circuit from the tip and ring conductors of the tieline.

Another feature of theinvention is an arrangement 1n outgoing trunksemployed in I systems of thiskind and in thecord circuit whereby-aringing bridge normally connected across the tip and ring, conductors ofthe trunk is automatically removed during dialing. This isaccoi'nplished by'haviiig a relay in the sleeve circuit of the trunkoperate to remove the bridge when the dial is ofl normal, the off-normalcontacts of the dial causinga low resistance shunt around a winding ofthe usual battery feed relay to be established for the operation 0 therelay in the trunk circuit.

In tie lines for private branch exchange systems of the above typesurges may occur on the line to cause momentaryoperations of thealternating current responsive relay used for lighting the line lamp.Means has heretofore been provided for delaying the lighting of thislamp. This'means usually includes a slow-to-operate relay and atslowto-release relay. r

An arrangement of this kind is satisfactory when the voltage ofthebattery supply is comparatively low as the slow-to-operate relaywillthen function, properly. In modern telephone service a'highervoltage battery is desirable and the slowto-'operate relay will notoperate suiliciently slow under these oircumstancesto delay theoperation of the line signal. t is therefore a further feature of thisinvention to provide an ar-' rangement whereby only slow-to-releaserelays ai'e employed in the circuit arrangement for delayingtheoperation of the-line signal. The operation of the signal maytherefore be delayfor the proper interval independent of thecharacteristics ofthe voltage of the operation current.- I

This invention has oeenillustrated 1n the accompanying drawings inwhich,

Fig. 1 shows acord circuit A and an associated' operators telephonecircuit at a private branch exchange embodying features of andterminating in jacks at the private branch exchange and extending, toother pri vate branchexchanges. The figures may be arranged as shown in6, i

To explain the various features of this in i vention in connection withthese drawings,

descriptions will be made as follows: A call from the calling subscriberof line 1 over cord circuit A. in Fig. 1 and trunk 200 in Fig.2 to adistant exchange, the release of such a connection and a recall bythesubscriberv of line 1 of the operator before this connection has beentaken down; second, a call incom 111g over trunk 200 and answered by th0pand 24 to the operators set 17. [he ring con-- erator; third, anoutgoing call from the 0perator over the tie line shown in Fig. 3;

fourth, an outgoingcall over the tie line shown in Fig. 4, and fifth, acall incoming over the tie line shown in Fig. 5. Referring now to theestablishing of a connection from the subscriber of line 1 through cordA over trunk 200 to the distant exchange, the calling subscriber bylifting his receiver off the switchliook' causes theli'ne relay 2 to beoperated to light the line lam 8 inthe usual manner. This call isanswered by the operator of cord A by inserting plug nals of plug 5 andiack 6, subscribers loop,

tip terminals of jack 6 and plug 5, upper contacts of ringing key 12,upper winding of relay 7, upper middle normal contacts of dialing key11, upper winding of relay 8 to ground at lower outer back contacts ofrelay 9. Relay 811 operating performs no useful-* function at this time.Relay 7 opens the 011'- cuit for supervisory lamp 15 which was closed inthe sleeve circuit to ground onjack 6, when plug 5 was inserted therein.Ifit s assumedthat the talking key 16 has been op-'- 3139 erated beforethe call was answered to assomate the operators telephone 17 with thecord circuit, the supervisory lamp 18 will not operate in the abovementioned sleeve circuit as the circuit therefor'will be opened due tothe operation of relay 19, as will hereinafter be described,

With the operators telephone set connected through plug 5 and jack 6 tothe calling subscribers line the operator will now ascertain the desirednumber and if a connection to a distant exchangeis desired the operatorwill insertrplug 20 into the jack 201 of the trunk 200 leading to thisdistant exchange.

The immediate effect of this operation will 11 be the operation of relay21 from battery,

' winding of relay 203, contacts of jack 201, the

sleeve terminals of this jack and plug 20, upper inner normal contactsof dialing key 11, winding of relay 21 to ground. Relay 203 beingmarginal in character will not operate in this circuit. Relayineperating disconnects the calling subscribers line from the talkingconnection through condensers ductor is connected at the upper outerarmature and front contact of relay 21 to the contact of the. upperinnerarmature of relay 8 and the front contact of the upper outerarmatureof relay 9. Relay'21 also disconnects" 13 sleeve terminals ofplug 5 and jack 6 to battery at its upper inner armature and backcontact from the upper winding of relay 19 and connects it to thewinding of relay 9. Finally, relay 21 opens the sleeve circuit for lamp18 at the lower inner armature and back contact. The operation of relay21 closes a short circuit around the windings of relay 7 to cause it torelease while relay 8 is maintained operated. This short circuit may betraced from battery, upper inner armature and back contact of relay 9,lower winding of relay 8, upper outer armature and front contact ofrelay 21, upper inner armature and front contact of relay 8, upperwinding of this relay to ground at the lower outer armature and backcontact of relay 9. The purpose of this short circuit across the tip andring conductors is to prevent a click through the calling subscribersreceiver which occurs when battery and ground is removed later by theoperation of relay 9, and to prevent this relay from operating untilrelay 7 has released. When relay 7 releases it closes a circuit forrelay 9 as follows: tery, upper makebefore-break contact of relay 21,winding of relay 9, upper inner armature and back contact of relay 25,lower makebefore-breakcontact of relay 8, lower armature and backcontact of relay 7, sleeve terminals of plug 5 and jack 6 to ground atthe lower made contacts of jack 6. Relay 9 in operating disconnectsbattery at its upper ar1na ture and back contact from the ring conductorof the calling subscribers line and ground at its lower outer armatureand back contact from the tip conductor. This relay in operating alsoconnects the lower winding of relay 19 across thetip and ring conductorsas connected to the normal inner upper and lower contacts of talking key16 to the tip and ring conductorsof the plug 20. This will serve as aholding bridge after the connectlon has been established Relay 9 alsoconnects the tip and ring conductors from plug 5 to plug 20; at itsupper outer armature and front contact for the tip conductor and at itsmiddle lower make-b'efore-break contacts for the ring conductor. Whenre]ay 9 operates the above mentioned short circuit for relay 7 and theholding circuit for relay 8 is opened and this relay now releases. Whenrelay 8 releases it permits relay 7 to operate over the loop extendingthrough plug 26 and ack 201 to the battery and ground at the distantexchange over trunk 200. As relay 8 is now re leased relay 25v isoperated over a circuit as follows: Battery, upper ma :e-before-breakcontact of relay 21, upper outer armature and back contact of relay 8,winning of relay 25, lower 1nner armature and back contact of thisrelay, armature and front contact of relay 7,

ground on jack 6. Relay 25 in operating provides a locking circuit foritself through its 7 lower make-before-break contact and lower armatureand front contact of relay 9 to the ground on jack 6' under control ofrelay 9. Relay 25 in operating opened at its upper outer armature andback contact the holding bridge through the lower Winding of relay 19and by closing its upper make-beforebreak contacts transfers the controlof relay 9 to the sleeve circuit closed by relay 7.

If the call is to be extended to a dial central office the operator willdial the desired subscribers line as follows: As the talking and dialkey 16 is operated the immediate effect will be the operation of relays26 and 27 over a circuit from battery, winding of relay 203, the sleevecircuit of jack 201 and plug 20, upper inner normal contacts of key 11,upper outer made contacts of key 16, lower winding of relay 26, windingof relay 27, lower inner armature and back contact of relay 31 toground. The relay 27 operates first and short-circuits the receiver ofthe operators set 17 at its armature and front contact. Relay 26 inoperating also shortcircuits the receiver at its upper armature andfront contact. The purpose. of this will be described hereinafter. Relay26 closes a circuit for the operation of relay 29 from battery, windingof relay 29, upper outer armature and back contact of relay 30, upperouter armature and back contact. of relay 31 to ground at the lowerarmature and front contact of relay 26. Relay 29 in operating opens atits upper inner armature and front contact a circuit for relay 31 andcloses a ringing tripping bridge across the tip and ring conductors ofthe cord circuit at its lower outer armature and front contact throughthe right hand winding or retardation coil 32 and across the left handwinding of repeating coil 33. This bridge performs no useful function atthis time but on incoming calls over trunk 200 it trips the ringing.Relay 29 in operating also closes a circuit for relay 30 from battery,winding of relay 30, lower inner armature and front contact and upperouter armature and front contact of relay 29, upper outer armature andback contact of relay 30 to ground at relay 26. Relay 30 in operatingprovides a: locking circuit for itself to this ground at relay 20through its upper make-before-break contacts. Relay 30 also closes asecond connection for the above mentioned tripping bridge through itslower outer armature and front contact. Relay 30 also short-circuits thereceiver at the lower inner armature and front contact in multiple withthe upper armature and front contacts of relays 26 and 27. Relay 30 alsoopens the circuit for relay 29 at its upper outer armature and backcontact armature and back contact of-relay 29, up-

per inner arinature and front contact of reoperate and relay is slow inreleasing.

Relay 30 in releasing opens the tripping bridge closed at its lowerouterarmature and front. contact, as well as the short circuit for thereceiver through its lower inner armature and front contact. Theoperating times of relays 26, 27 and 31 and the releasing times ofrelays 29 and 30 are such as to allow the tripping bridge to causetripping functions at the distant exchange to take place'before theoperatofls receiver is connected to the telephone circuit in order toprevent the operator hearing. clicks which may occur due to theseoperations. Due to the operation of relay 31 and release of relay 30 theoperators receiver Wlll now be connected to the talkingkey 16 over thet1p and ring conductors over the trunk 200 and a dial tone will then beheard by the operator when the central office equipment is ready toreceive dial pulses.

When, now, the operator actuates the dial the off-normal contacts ofthedial open the circuit for relay 31. This relay in releasing againshort-circuits the receiver. Relay 27 may be released at this time dueto the high resistanceof the upperwinding of relay 26. At the releasejofrelay 31 the upper high resistance winding of relay 26 is shunted by theestablishing of the connection to ground at the lower inner armature andback contact of relay 31 and relay 27 reoperated. When relay 31 releasesrelays 29 and 30 are again operated to maintain the short circult forthe receiver independent of relays 26 and 31. Relay- 31 in releasingalso closes the circuit for the operation of relays 36 .and 37. Relay 36is operated by a circuit from battery, winding of relay 36, upper outerarmature and back contact of relay 38, lower outer armature and backcontact of relay 31, ofi-normal'contacts of dial 35 to ground at thelower armature. and front contact of relay 26. The circuit for relay 37may be traced from battery winding of this relay over the same circuitto ground at relay 26. Relay 37 in operating short-circuits the middleand left hand windings of the retardation coil 32, by closing theconnection throughits low-er'outer armature and front contact andopensthe connection to ground from the transmitter circuit applied at thelowerouter make contact ofkey 16 through.

the upper outer armature and back contact of relay 37. Relay 37.connects this. ground through this armature and the correspondingfront'contact to the connection between the lower winding of relay 26and the winding of relay 27. Relay 27 is thereby. short ciricuited whichcauses the operation of the marginal relay 203 in the trunk circuit 200.Relay 203 in operating opens the bridge through the. ringing relay 20 1to prevent this bridge from interfering with the impulses outgoing overthe trunk 200 when dialing again. It will be noted that the relays 30and 31 while placing a short circuit on the receiver at this timeprevent the operator hearing any clicks due to the operation of relays36 and 37. Relay 36 in operating connects ashortcircuit across themiddle winding of the retardation coil 32 to prepare a low resistancebridge across the trunk circuit when the dial returns to normal. Thisbridge will extend between the, tip and ring conductors through theupper make-beforewbreakcontacts of, relay 36 and. the left hand windingof retardation coil-32. Relay 36 also in operating opens the connectionbetween the plugs 5 and 20 to the tip'and ring conductors at the upperand lower armatures and back contacts. This relayalso connects the tipand ring conductors from plug 5 through these armatures and thecorresponding front contacts through the winding of relay 38 to batteryand ground. Relay 38 now operates over the loop to the calling stationif the receiver is still ofi the hook or through the bridge in the cordcircuit established by the operation of relay 9, as hereinbeforementioned. -Re- I lay 38 in operating opensa circuit at its upper outerarmature and back-contact for relay 36 from the off-normal contact ofthe dial 35 and locks up this, relay through the upper make-before-breakcontacts toground.

V The dial may now return-to normal opening and, closing theimpulsecontact accord ingto the digit selected. The line connection through tothe distant exchange closed by relay 37 is thereby interrupted to beginthe selection of the desired subscribersline in the usual manner. Itshould be noted that this connection is free from all encumbrances asthe bridge in the trunk circuit is removed from across the line and therepeating coil 33 and retardation coil 32 are short-circuited by theoperation of relay 37 and the calling subscribers circuit is removed bythe operation of relay 36. \Vhen the dial is restored to normal theoff-normal springs open the circuit for relay 37 which now releases andrem-ovesa short-circuit from the left and middle windings of retardationcoil 32 and connectsa ground to the transmittercircuit at-its upperouter armature and back contact. The normally closed off-normal springsof the dial 35 now close-the circuit through the contacts of relays 30and 29 for relay 31*- which operates and opens the short circuit for thereceiver applied by relay 26.. A short.- oi-rcuit however is stillmaintained byrelay 30. Relay 31 in operating closes the same lockingcircuit for itself and opens the circuit for relay 30 which releasesslowly and removes theshort circuit from the receiver. Theslow-to-operate characteristic of relay 31 and slow-to-releas-echaracteristic of relay 3O prevent the operator hearing clicks due tothe dialing operations. Relays 36 and 38 remain operated undercontro-l'of the key 16. The calling subscriber may now talk to theoperator and to the central office when relay 30 releases, thisconnection being -estab lished to condensers 39 and 40. The centraloflice circuit is held operated by the bridge 7 through the left handwinding of the retaring key 16 is operated. hen the subscriber at'thecalling'station again removes the receiver from the switchhook lamp isex tinguished and the call proceeds in the usual manner. At the end of-aconversation when the lamp 15 is lighted indicating that thecalling'subscriber has hung up his receiverthe operator may remove theplug from the trunk and restore the circuits to normal; Then relay?releases to' light lamp 15 the connection through the tip and ringconductors from plugs 5 to 20'is' split and local battery and ground areconnected to the tip and ring con ductors leading to the callingsubscriber over plug 5 and jack'6 while a bridge isconnected across thetip and ring conductors leading to the distant exchanges through plug20. This is to prevent the calling subscribers station from beingsignaled on incoming calls from the central oliice in case theconnection has not been taken down immediately after disconnection bythe calling subscriber. The local battery and ground is supplied to thecalling subscribers line to permit this subscriber to originate anewcall after disconnection, When both cords are removed from the jack allrelays restore to normal. The operations are as follows: lVhen thecalling subscriber hangs up his receiver relay 7 releases causingtherelease of relay 9. i This splitsthe cord atthe upper outer armatureconnects battery at its upper inner armature and back contact to the tipconductor and ground to the ring conductor at its lower outer armatureand back contacts through the windings of relays 8 and 7. It should benoted however that the upper winding of re lay 8 is short-circuitedthrough the. upper outer armature and front contact of relay by theabove mentioned ground to prevent the false operation of relay 8 whenrelay 9 is released. At this time a surge of current may occur due tothis battery and ground connection charging the usual condenser in thesubscribers set at the calling station. This surge of current, whichwould pass through the lower winding of relay 8 would have thetendencytocause the relay 8 to. operate and thereby cause the release ofrelay 25 but is prevented from so doing by the short circuit aroundtheupper winding of relay 8. In other words, this short circuit of theupper windingca-used by the operat ed condition of relay 25 prevents thenormal circuit through the two windings of rela 8 from being completedon the release of relay 9, while the circuit from battery to groundthrough the lower winding of relay 8 is not sufiicient to operate thisrelay.

If now thecalling subscriber removes his receiver from the switehhookunder this condition relays 8 and 7 will both be operated. Relay 8 isoperated in this case by the current passing through the lower windingof relay 8. Relay 8 in operating opensthe circuit for relay 25 which nowreleases. Relay 8 in operating also short-circuits as hereinbeforedescribed the calling subscribers line and relay 7'. Relay 9 is thenoperated, due to release of relays 'Z and 25 and operation of relay 8,from battery, upper inner make-before-breakcontacts of relay 21, windingof relay 9, upper inner armature and back contact of' relay 25', lowermake-before--break contacts of relay 8, armature and back contact ofrelay 7 to ground over thesleeve terminals of plug 5. and ack 6to-ground. Relay 9 in operating connects the central ofiice battery andground through the windings of relay 7 and the calling subscribers-loopcausing relay7'tooperate and relay 8 to release. Relay 7 inoperatingextinguishes the lamp 15 and closes a circuit for thereoperation of relay 25 as hereinbefore described. Relay 25 in operatingprovidesthe usual lockin circuit for itself under control of relay 9 andrelay 7 and places relay 9' under control of relay 7. Under thesecircumstances therefore it is evident that any delay of the operation ofrelay 7' from the central ofiice source will not interfere with theproper-functioningof relay 9 in establishing the through connection.

If the call is incoming over trunk 200 the ringing relay 204 will beoperated; This relay in turn closes a circuit for the operation of thealternating current responsive relay 206. This relay in operatingprovides a lock- 1ng c1rcu1t for itself through its'upper winding" andupper armature and front contact guishes signal 207. lVhen relay 21 isoperated over the sleeve circuit as hereinbefore traced thisrelay opensthe tip and ring conductor connection between plugs and 5 throughcondensers 23 and 24. Relay 9 is now also operated from battery,uppermakebefore-break contacts of relay 21, winding of relay9, upper innerarmature and back con tact of relay to ground at the lower arl'na tureand front contact of relay 8. Relay 9 in operating disconnects at thelower makebefore-break contacts ground for the tip conductor and batteryfrom the ring conductor leading to plug 5. It also connects "the lowerwinding of relay 19 across the tip and ring conductors leading to theplug 20 as a holding bridge and connects the tip and ring con ductorsfrom plug 20 to plug 5. Itwill be noted that in order to prevent theoperator from receiving clicks while answering this call her telephonereceiver will be inonientarily short-circuited due to theoperations ofthe relays 26, 27, 29, and 31 as hereinbefore described. That is, itwill be maintained short-circuit-ed between the operation of relays 26and 31. same regardless of whether the key 16 is op erated to answer thecall before or after the plug 20 is inserted in jack 201. In either casethe ringing will'be tripped by the bridge established as hereinbeforedescribed through the right hand winding of retardation coil 32' by theoperation of relay 29 and the receiver will be short-circuited toprevent the operator from hearing clicks incident to the answering ofthe call. When the key 16 is restored to normal the connection is cutthrough and when plug 5 is inserted into the jack of the desired line,lamp 15 is lighted. When the desired subscriber answers relay 7 isoperated to extinguish it and cause the operation of relay 25 ashereinbefore described. Relay 25 in operating provides alocking circuitfor itself under control of key 16, and opens the holding bridgeconsisting of the primary winding of relay 19 from across the trunk 200and places relay 9 under control of relay 7.

If a connection is established to another private branch exchangeoverthe tie line 300 shown in'Fi 3 from a subscriber through cord circuit 3;the following operations will take place: The operations in the cordcir- These relays operate the.

l Q f a V cuit are the same as hereinbefore described for the extendingof a connection over trunk 200. lVhen plug 20 is inserted into jack 301relay 302 operates over acircuit from battery, winding of this relay toground at the lower contacts closed by jack 301. Relay 302 in operatingdisconnects the jack from the trunk 300 andestablishes a circuit forrelay 304 from battery, winding of this relay, lower inner armature andfront contact of relay 302 over the sleeve circuits of jack 301 and plug"20 to ground through the winding of relay 21 as hereinbefore described.Relay 304 in operating closes an obvious circuit for the operation of,relay 305. This relay connects battery and ground'through theretardationcoil 306 for the tip and ring condoctors and the left handwindings of repeating coil307. When now the ringing key 40 is operatedto ring the distant end of the tie line, the ringing responsive relay308 bridged across the tip and ring conductors is operated by ringingcurrent applied by key 40. Relay 308 in operating short-circuits relay302 at'its lower armature and front contact and relay 302 inv releasingcauses the release of relays 304 and 305. Relay 302 in releasing alsodisconnects the windings of the repeating coil 307 from the line at theupper inner and middle arinatures and front contacts and connects thetip and ring conductors through past the repeating coil 30'? at theupper and lower outer armatures and back contacts. The tie line is nowcleared from all encume brances so that-ringing willpass through the tipand ring conductors directly out over the tie line. l/Vhen ringingceases relay 308 is released and relays 302, 304' and 305 reoperated toreconnect the repeating coil 307 in the line for speech transmission;

The operation of the tie line 400 shown in Fig. 4 will now be describedin connecti on with'an outgoing call. The operation of the cord circuitA is the same as hereinbefore desc ibed in connection with an outgoingcall over trunk. 200. lNhen the plug 20 is in:

serted in the talking'jaclr 401, relay 402 is operated over an obviouscircuit closed by jack 401. vRelay 402 in operating connects the relay403 the upper inner armature and front contact to the open sleevecontacts of the dial jack 405. Relay'406 is connected through the upperouter armature and front contact of relay 402 to the sleeve of jack 401and relay 403 is operated by an obvious circuit closed through the lowerinner armature and front contact to ground. The operation of relay 407closes a circuit for the lighting of line lamp 408 from battery, lamp403, upper armature and front contact-of relay 409, upper armature andback contact of relay 407 to ground. 5 Relay 406 now operates over thesleeve circuit in series with relay21 andcloses the circuit for theoperation of relay .410. Relay 410in operating. connects battery andground through the retardation co 1-11 to the tip and ring conductors ofthe 401 to supply tall 'ng and supervisory battery for the cord le it.

Relay 402 also closes at its lower outer armature and front contact abridgeacross the tip and ring conductors of line 400outgoing torstelephone set in cord A.

to the distant exchange, through the upper winding of relay 409 andretardation coil'412 to prepare the circuit at a distant exchange fordialing. lVhen the distant exchange is.

ready for reception of dial pulses a dialing tone will be transmittedthrough the condensers 418 and 414 over acl: 408 to the opera- Theoperator will then insert a plug corresponding to plug :-of anothercor'dcircuit into the dialjach 405 for the purpose of dialing the distant exchange. Relay 403 is thereby operated over tne connection established byrelay 402 in series with the relay 21 in the second cord circuit. Relay403 in operating closes acircuit for the operation of relay 415 frombattery, winding of this relay, upper inner iarmature and back contactof relay 416,

armature and front contact of re if nects the midpoint between the twowindings of relay 417. at its upper armature and front contact to thetip conduct-or of the dial jack.

' If now relay 21 in the cord circuit has not operated at this timerelay 417 will operate .40: a

3 the battery and ground over the tip and ring conductors from the cordcircuit causes a difference in potential between the two windings ofrelay 417. Relay 41'? in operating opens at one poiir the circuit forrelay 416 i at its lower armature and back contact to prevent this relayfrom operatingwhen relay 418 operates to close another point of thiscircuit. Relay 418 will operate over an obvious circuit closed by theoperation ofjrelay Belay 4 8 in operating prepares this operating pahfor relay 416 at lower outer armature and front contact and opens alookingcircuit for relay-410 at its lower inner contacts. Relay 418 alsoconnects a short circuit across the tip and ring conductors of the tieline at its upper armature and front contact the purpose of which willbe described hereinafter. Relay 418 further opens the ring conductor ofthe dial jack from the lower armature and front contact of relay 416 atits upper inner contacts.

These relays now remain operated until the circuit forrelay 4fl6'at itslower armature and front contact. Relay 416 operates and prepares adialing circuit through the tip and ring conductorsof the dial jack asfollows: As relay 41.6 in operating opens the operating circuit forrelay 415 at its upper inner armature and back contact relay 415releases, but as it is slow in releasing the locking circuit for relay416 controlled by relay 418 is prevented from closing in case relay 416should be operated momentarily when ground is removed from the tipconductor in the cord circuit before the battery is removed which causesrelay 417 to release and reoperate due to the change of potential acrossits winding. l/Vhen relay 415 releases fully it removes the shortcircuit from the tip and ring conductors of the dial jack 405 at itslower inner armature and front contact and disconnects relay 417 fromthe dial jack tip and ring conductors. Relay 415 also opens the circuitfor relay 418 and connects the tip conductor of the dial jack to the tipconductor of the line 400 through its'upper armature and back contactand the upper outer armature and front contact of relay 416. Relay 418in releasing closes the looking circuit for relay 416 to the ground atrelay 408 before it opens the operating circuit for relay 416 and closesthe ring conductor from the dial jack to the line 400 through its innerupper contacts and the lower armature and front contact of relay 416before it opens the short circuit across the tip and ring conductors ofthe line. The action of relay 415 in closing the tip conductor throughto the line and the relay 418in closing the ring conductor through tothe line before relay 418 removes the short circuit from the line is toprevent the possibility of an open circuit appearing at this time andcausing a false impulse to be sent to the distant tie line circuit. Dialtone may now beheard by the operator provided the talking dial'key isoperated .on the cord circuit connected to the dial jack; The operatornow dials the desired number at the; distant private branch exchange. I

After dialing is completed the operator removes the plug of the cordcircuit used for dialing from jack 405 causing relay 403 to releasewhich in turn opens the locking circuit for relay 416. Relay-416 inreleasing reestablishes the talking connection over the trunk 400 tojack 401 through the cord circuit connected to this jack. Then thecalled subscriber answers the call the direction of the current flowingfrom the distant private branch exchange is reversed causing theoperation of polarized relay 409 to extinguish the lamp 408. Relay 407now locks under control of relay 409 by the circuit established atthexupper armature and front contact of relay 409 to preventlamp 408from lighting falsely on disconnection at this exchange.

release of relay 409. If this occurs while the I; plug is still insertedin the j ack 401, the line lamp 408 will light asa disconnect signal. Ifthe plug is removed from this jack before the distant exchangedisconnects the. short circuit is removed from the lower winding ofrelay 409 by the release of relay 402 to cause an increase in theresistance of the line and thereby in the usual manner release theconnection at the distant exchange. Relays 409 and 407 remain operatedto prevent the lighting of the line 1311111408 at this time. i

to a subscriber in the private branch exchange over cord'A. When thedistant private branch operator applies ringing current to this tie linerelay 501'is operated. This relay closes a circuit forrelay 503.. "Relay501 vibrates in response to the ringing cure rent and opens and closesthe circuit for relay 503 but this relay remains operated steadilybecause of the shunting resistance504 and capacity 506. The -retardationcoil 507 and capacity 506 are used to preventthe buzzing circuit fromcausing noise on the usual bate tery feeding'systenij Relay 503 'in'operating closes a circuit for the operation of relay 510 from battery,winding of relay 5 10, lower make-before-break contacts of relay 511,upper inner contacts of relay 512 to ground at the armature and frontcontact of relay 503. Relay 510 closes a circuit for relay 511 frombattery, winding of relay 511, lower armature and front contact of relay510, inner ipper contacts of relay 512 to ground at the armature andfront contact of relay 5,03. Belay 511 in operating provides a lockingcircuit independent of relay 510, the circuit of which is opened byrelay 511. Relay510is slow in releasing and therefore delays the.closing of a circuit for the operation ofrelay 512from battery, lowerwinding of relay 512, upper armature and back contact of relay. 510,upper armature and front contactof relay'511 to ground at relay 503.Relay 511 also closes a momentary locking circuit for itself through itslower armature and front contact to ground at relay 503. This circuitopened on the operation of relay 512 "a n d"as relay 510 opened theoriginal energizing circuit relay 511 will now release. Relay 511completes the obvious circuit for. lighting s gnal 515 closed by relay512. Relay 511 is slow in releasing. The purpose ofthe slow-toreleasecharacteristics of relays 510 and511 is to hold the circuit for signal515 open long enough to prevent the false lighting of this 'a cordcircuit,'a relay for controlling the consignal in case relay 501operates on surges such as may'occur upon disconnection; Relay 512 inoperating closes a locking circuit" for 05 itself from battery,resistance 504, upper A description will now be made of aycall' incomingover tie line 500 shown in Fig. 5

winding of relay 512, upper armature and back contact of relay 517,lower inner armature and front contact of relay 512 to ground at thelower outer armature and back contact of relay 511. This is tomaintainrelay 512 operated. after the original energizing circuittherefor is opened by the release of relay 511. The relay 512 is heldoperated between the opening of the original circuit and the closing ofthe locking circuit by the circuit established by its upper armature andfront contact for the lower winding to ground at relay 503. In otherwords, the

. period'of delay in the operation of lamp 550 depends solely on theslow-to-release characteristics of relays 510 and 511 independent ofthevoltage conditions on the line. To answerthis call plug 20'is insertedinto jack 516. This causes the operation of relay 517 over a circuitclosed by the jack 516. Relay .517 iii operating opens the lockingcircuit forrelay 512 and-this relay in releasing opens the circuit forlamp 515. Relay 517 also establishes a connection from ground for thesleeve circuit to provide the "usual supervision on the cord circuit.The establishing of a connection to the desired subscribers line in theprivate branch exchange may now proceed in the usual manner through thecord circuit A. Y

Although this invention has been disclosed .in connection with but asingle system, it

the hanging up of the receiver of. the: telephone set of one line forreleasing said re lay to break the continuity of said cord circuit.

2.. In a telephone system, subscribers lines,

a cord circuit,v a slow-t-o-release relay for-- controlling thecontinuity of said cordcircuit, means responsiveto the establishing of aconnection between two lines through said cord CllClllllfOI operatingsaid relay to establislrcontinuity-in the said cord circuit, and.

means responsive to the hanging up of the receiver of the telephone-setof one line. for

permitting the release-of said relay inac- -cordance with itsslow-to-release characteristics.

3. In atelephone system, subscribers lines,

lay havinggits windings included in the tip and ring'conductors of thecord circuit, means responsive to the establishingof a connectionbetween two lines through said cord vcircuit for operating said relaysindependently, means for'transferring the control over the firstmentioned relay to the supervisory relay to maintain it operated whenthe supervisory relay is operated, and means responsive to the hangingup of the receiver of the telephoneset of one line for releasing thesupervisory relay to release thefirst mentioned relay to break thecontinuity in the cord circuit.

4. In a telephone system, lines, trunks, a cord circuit, a relay forcontrolling the continuity of said cord circuit, a supervisory relay insaid cord circuit, means for operating said supervisory relay on theconnection of the cord circuit to a line, means for operating said firstmentioned relay on the connection of the cord circuit to a trunk, meansresponsive to the operation of said first mentioned relay for releasingthe supervisory relay and for establishing the continuity of said cordcircuit, means .for reoperating said supervisory relay, and means fortransferring the control of said first mentioned relay to saidsupervisory relay responsive tothe reoperation ofsaid supervisory relay.

' .5. In a telephone system, lines, a cord circuit, a relay forcontrolling the continuity of said cord circuit, means responsive to theestablishing of a connection between two lines through said cord circuitfor operating said relay to establish continuity in said cord circuit, asupervisory relay in said cord circuit, means for transferring thecontrol oversaid first mentioned relay to said supervisory relay, acurrent supply in said cord circuit, a current supply in one of saidlines, means for transferring the control over said supervisory relayfrom the current supply in the cord circuitto the current supply in saidline, and means for preventing the first mentioned relay from releasingduring the transfer of control of said supervisory relay from onecurrent supply to the other.

6. In a telephone system, a subscribers line terminating in a telephoneset including acondenser, a trunk, means for connecting said line andtrunk, a first relay, a current'supply, a second relay having twowindings normally connected in circuit between said current supply andline, means for releasing said first relay when said subscriber hangs uphis receiver. to disconnect said trunk fromsaid line and connecting thecurrent supply to'the subscribers line through the windings of saidsecond relay, a third relay, 7

means for actuating saidthird relay in response to the establishing of aconnection,

means for holding said third relay under control of said second relay,and means for short-circuiting one winding of said second relay undercontrol ofsaid third relay for preventing saidsecond relay fromoperating from the switchhook for reestablishing a connection throughthe cord circuitindependent of the supervisory relay.

r 8. In a telephone system, a subscribers line, a cord circuit, a trunk,means for es tablishing a connection between said subscribers line andtrunk through the cord circuit, 'a supervisory relay, means forreleasing said relay in response to the subscriber replacing. hisreceiver on the switchho ok, a

splittingrelay, means for releasing said splitting relay to split theconnection through the cord circuit in response to the release or" thesupervisory relay, and means thereafter responsive to the removing ofthe receiver from the switchhook for reestablishing a connection throughthe cord by the reoperation of the splittingrelay independent of thesupervisory relay.

9. In a telephone system, a subscribers line, a cord circuit, a trunk, asupervisory relay, means for establishing a connection between said Isubscribers line and trunk through said cord circuit under control ofsaid supervisory relay, means responsive to the subscriber replacing hisreceiver on the switchhook' for splitting the connection through thecord'circuit-under the control of said supervisory relay, meansresponsive to the subscriber again removing his receiver from theswitchhook forreestablishingthe connection through the cord circuitindependent of the supervisory relay, a current supply in the trunkcircuit, means for connectingthis current supply to the cord circuitafter the reestablishing of the connectionthrough the cord circuit,means respons siveto this connection of'the current supply .foroperating the supervisory relay, and

means responsive to this operation of the superv sory relay for placingthe splitting means under control of said supervisory 10. Ina telephonesystem, a line, trunks, a cord circuit for connecting a line and atrunk, a current supply in said cord circuit,

means responsive to the connection of the cord circuit to a subscribersline forconnecting said supply to a subscribers line, means responsiveto the connecting of the cord circuit ,to a trunk'for short-circuitingsaid subscribers line, for removing said supply from said cord circuit,for establishing a bridge across the tip and ring conductors of saidcord circuit for removing said short circuit, and for connecting the tipand ring conductors of the cord circuit through from the subscribersline to the trunk, a current supply in said connected trunk, and meansresponsive to the removal of the short circuit and the connection of theti and rin conductors through the cord circuit for the passage ofcurrent therethroug-h from said supply in the trunk for removing thebridge.

11. In a telephone system, lines, trunks, a cord circuit for connectinga line and a trunk, a battery and ground connection, means responsive tothe establishing of a connection between the cord and the subscribersline for connecting said battery and ground connection to the tip andtin g conductors of the subscribers line, means responsive to theestablishing of a connection between the cord circuit and the trunk forshort-circuiting the line, for removing the battery and groundconnection from the cord circuit, for applying a bridge across the tipand ring conductors, for removing the short circuit, and for connectingthe tip and ring conductors through to the trunk, a battery and groundconnection in the trunk, and a relay means responsive to current fromsaid last mentioned battery and ground connection for re moving thebridge.

12. In a telephone system, subscribers lines, trunks, a cord circuit forconnecting subscribers lines with trunks, an operated telephone set,means for associating said telephone set with a cord circuit, meansresponsive to the connection of a cord circuit to a trunk and theassociation of thetelephone set to said cord circuit forshort-circuiting the receiver in said set, for establishing abridgeacross the tip and ring conductors of the cord circuit and formaintaining said short circuit and bridge for a short interval.

13. In a telephone system, a calling line, a trunk, a cord circuit forconnecting said line to said trunk, an operators telephone set, meansfor opening the connection through the tip and ring conductors of thecord circuit when the subscriber hangs up the receiver on the switchhookto release a connection, means for connecting the operators telephoneset to the part of the cord circuit connected to the trunk, means forshort-circuiting the operators receiver in response to the connectionrofthe operators telephone set to said cord, meansfor establishing a bridgeacross the tip and ring conductors of the part of the cord circuitconnected to the trunk, and means for maintaining said short circuit andsaid bridge for a short interval thereafter.

14. In a telephone system, a cord circuit, a trunk, means for connectingthe cord circuit to the trunk, an operators telephone set,

means for connecting said telephone set to the cord circuit, meansresponsive to the connection of the cord circuit to the trunk andtheoperators telephone set to the cord cirmeans for connecting the cordcircuit to the trunk, means responsive to the connection of the cordcircuit to the trunk and the set to the cord circuit,for-shortcircuitingthereceiver and for establishing a bridge across thetip and ring conductors of the trunk to operate said ringing trip relay,and 'means for removing said bridge and opening the short circuit ashort interval thereafter.

16.In atelephone system, a cord circuit, a trunk, means .for connectingthe cord circuit to the trunk, an operators telephone set, a dial, meansfor connecting said set and dial to the cord circuit, and meansthereafter responsive to the operation of the dial for short-circuitingthe receiver during the dialing and for a short interval thereafter.

17. In a telephone system, a cord circuit. a trunk, means for connectingthe cord circuit to the trunk, an operators telephone set. a dial, meansfor connecting said set and dial to the cord circuit, means responsiveto said connection of the set and dial to the cord circuit forshort-circuiting the receiver and establishing a bridge across the tipand ring conductors of the cord circuit for a short interval, and meansthereafter responsive to the operation of the dial for short-circuitingthe receiver during the dialing and for a short interval thereafter.

18. In a telephone system, a trunk, a cord clrcuit, means for connectingsaid cord cir cuit to said trunk, a repeating coil in said trunk, meansresponsive to the establishing of a connection between the cord and thetrunk for connecting said repeating coil across the conductors of saidtrunk, a ringing responsive relay in said trunk, means for applyingringing current to said trunk for operating said relay, and meansresponsive to the operation of said relay for removing the repeatingcoil from across the conductors of said trunk.

19. In a telephone system, a tie line having atalking connection andadialing connection, means for establishing the talkin connection to thetie line and means for esta lislringthe dialing connection to the'tieline, means responsive to the establishing of the dialing connection forshort-oircuiting it and for short-circuiting the tie line, a dial, meansfor connecting said dial to the dialing connection, and means responsiveto said connec tion of the dial for opening the talking connection, forremoving the short circuit from the dialing connection, for connectingthe tip conductor through from the dialing connection to the tie line,for connecting the ring conductor through from the dialing connection tothe tie line, and for removing the short circuit from the tie line.

20. In a telephone system, a trunk, -a cord circuit, a ringing bridgeacross the conductors of said trunk, a dial associated With said cord,means responsive to the moving of the dial off normal for removing saidringing bridge from across the conductors of said trunk.

21. In a telephone system, a tie line, a relay in said tie line, asignal, and means responsive to the operation of said relay foractuating said signal a short interval after the operation of the relay,said means including only sloW-to-release relays.

In witness whereof, I hereunto subscribe my name this 27th day of May,1931.

LANGFORD J. BOXVNE,

